1. Field of the Invention
The present invention relates to an ink jet recording apparatus, more specifically, an ink jet recording apparatus having a recording head mounted on a carriage moving while recording and an ink storage unit storing ink fluids also mounted on the carriage.
2. Description of the Related Art
As known generally, in an ink jet recording apparatus categorized as a serial type recording apparatus, an image is recorded on a recording medium such as recording sheets by ejecting ink fluids from a recording head in accordance with the movement of a carriage on which the recording head is mounted. This type of recording head has an orifice, an ink passage connected to the orifice in which an energy generation device is formed for generating thermal energy used for ejecting ink fluids, and a common fluid reservoir connected to the ink passage for storing ink fluids.
As for the ink storing unit such as an ink tank for storing ink fluids to be supplied to the recording head, there are two cases with respect to its installation into the recording apparatus; one is a case that the ink storing unit is mounted on a fixed position in the ink jet recording apparatus, and the other is a case that the ink storing unit is mounted on the carriage together with the recording head. In the former case, an ink supply route between the recording head and the ink storing unit is formed so as to trace the movement of the carriage during the recording operations.
In the latter case, it is possible to shorten the length of the ink supply route between the recording head and the ink storing unit. Therefore, this structure where the ink storing unit is mounted on the carriage is an adaptive structure for forming a small-sized and simplified recording apparatus.
Among variations of the structure in which the ink storing unit and the recording head are mounted together, what is adopted popularly today is a structure in which the recording head and the ink tank are integrally formed in a single assembly module so that both of the recording head and the ink tank can be replaced for new ones when the ink tank gets to be empty. This single-module structure makes it easier to fabricate and maintain the overall components of the recording apparatus.
In using this type of recording head fabricated with a single-module-structured ink tank, the following specific and generic problems occur.
At first, in order to determine the timing of replacing the recording head and the ink tank, the structure of the recording head is expected to have a sub-structure for detecting the amount of ink fluids remaining in the ink tank. Among the conventional ways and structures for detecting the amount of ink fluids, it is generally well known that the amount of ink fluids can be detected by measuring an electric resistance between two adjacent electrodes inserted into the ink tank.
However, in the above structure for detecting the amount of ink fluids, there is no habit to detect the amount of ink fluids in several levels discretely, and in such a case, there is another problem such that the number of electrodes required for establishing fine-pitched detection of the amount of ink fluids becomes larger, which makes the structure of the recording head more complex.
Next, in the conventional ink jet recording apparatus, there is no habit to control the ejection driving in response to the amount of ink fluids remaining in the ink tank. This may cause, in case the ink tank is almost empty, the refill of ink fluids from the common fluid reservoir to the ink passage not to be fully established response to ejecting ink fluids from the recording head, which is ultimately caused by the relative change in the pressure drop between the recording head and the ink tank. In such a case, in the conventional ink jet recording apparatus, any specific compensational control for ejecting ink fluids from the recording head is not performed. Owing to this, there may be ejection failures in prior art apparatus which leads to the reduction of the quality of recorded images.
Finally, though it is desirable to do some specific operations for verifying the ejection power of the replaced recording head when the recording head and the ink tank are replaced with new ones, there is no consideration in the conventional ink jet recording apparatus. In such a case, in order to verify the ejection power of the recording head, the operator must manipulate directly the recording apparatus, which may increase the load of the operator or may cause even some accident or damage in a series of operations unfamiliar to the operator.
A typical example of these specific operations is an ejection restoration operation. In the ejection restoration operation, ink fluids filled in the ink passage are forced to be removed from the orifice by evacuation or pressurization, or dummy ejection operations are performed in a designated position in the recording apparatus, both of which are used for removing viscous ink fluids remaining in the ink passage.
The reason why it is effective to perform ejection restoration operations when the recording head is replaced, is that the ink fluids in the neighboring area to the orifice get to be most viscous among ink fluids filled from the common fluid reservoir to the top of the orifice in case of using a single-module of a recording head and an ink tank.